1. Field of the Invention
The present invention broadly relates to a liquid jet recording head in which heat energy is applied to a liquid to cause a change in the state of the liquid, including generation of a bubble so that the liquid is discharged from a discharge port to form a liquid droplet flying toward a recording surface to attach to the same, thereby recording information such as letters, pictures and so forth. More particularly, the present invention is concerned with a process of producing a liquid jet recording head of the type described, a liquid jet recording head produced by the process, and a liquid jet recording apparatus incorporating such a recording head.
2. Related Background Art
Non-impact recording processes are becoming a matter of concern and interest because these processes can reduce the noise generated during recording to a negligibly low level. Among various kinds of non-impact recording processes, a process generally referred to as an ink (liquid) recording process is very promising because this process enables high-speed recording on ordinary paper sheets without requiring additional steps such as fixing. Hitherto, various liquid jet recording processes and devices have been proposed, some of which have already been put to commercial use while others are still being developed for practical use.
Among various types of liquid jet recording processes, a process of the type disclosed in, for example, Japanese Patent Laid-Open Publication No. 54-59936 and German Patent Laid-Open Publication (DOLS) 2843064 (which correspond to U.S. Pat. No. 4,723,129) is distinguished from other liquid jet recording processes in that the droplet-forming energy, i.e., the energy for forming and projecting a liquid droplet, is heat energy applied to the liquid.
More specifically, in the representative example of the recording process disclosed in the above-mentioned publications, the liquid being supplied with heat energy exhibits a change in its state, including a drastic increase in the volume, so that a physical force is generated to cause the liquid to be discharged in the form of a droplet from a discharge port of the recording head. The droplet flies towards a recording member and attaches to the same, thereby recording information.
In particular, the liquid jet recording process disclosed in the above-mentioned documents can be used quite conveniently in so called drop-on demand recording. In addition, this process facilitates design and production of a multi-port recording head in which a multiplicity of discharge ports are arrayed at a high density in full-line manner over the entire width of a recording region of a recording member, making it possible to produce a record image of high resolution and high degree of image quality.
This type of recording process is generally referred to as a "bubble jet recording process". FIGS. 1(A) and 1(B) show, by way of example, a typical liquid jet recording head of background art employing this type of recording process. More specifically, FIG. 1A is a plan view of a substrate having heat generating portions disposed in liquid channels for a recording liquid, which is in this case an ink, and leading to discharge ports, while FIG. 1B is a sectional view of the substrate taken along the line X'--Y' of FIG. 1A.
The substrate is denoted by 101, while 102 denotes a heat generating portion (referred to also as a "heater", hereinafter) which is disposed within the walls of each ink channel leading to an associated ink discharge port and capable of applying heat energy to the ink in the ink channel thereby generating a bubble. The heater 102 has a heat-generating resistor layer 107 to which are connected lead electrodes made of aluminum (Al) for applying a predetermined voltage across the heat-generating resistor 107. The heat-generating resistor layer 107 is carried by a carrier made of silicon (Si). Thus, the heater 102 is presented by the region between the pair of electrodes 103, 104.
A first upper protective layer 108 made of SiO.sub.2 covers the entire area over the lead electrodes 103, 104 and other portions. A major portion of the first upper protective layer 108 is further protected by a third upper protective layer 109 the surface of which contacts the ink. A second upper protective layer 110 covers the region where the heater 102 exists. The second upper protective layer 110 has a bubble-generating surface 112. The electrodes 103, 104 and the heat-generating resistor layer 107 in combination form an electro-thermal conversion element 111 which converts electrical energy into heat energy. In operation, when the bubble-generating surface 112 is heated by the heat generated by the heater 102, a bubble is formed in the ink contacting the bubble-generating surface 112 so that the ink is displaced and is discharged in the form of a droplet from the ink discharge port.
In the liquid jet recording head of bubble-jet type described hereinabove, a voltage is generated across the heater through the electrodes so as to cause the heater to generate heat which forms a bubble in the ink to discharge a droplet of ink from the discharge port. Thus, the generation and discharge of the ink droplet relies upon the principle of film boiling which generates a bubble. The state of the bubble-generating surface is therefore a very significant factor. Namely, stability of ink discharge is often impaired by the unstable generation of the bubble caused by such factors as the presence of minute convexities and concavities on the bubble-generating surface, i.e., the heater surface, attaching of a very thin film to the bubble-generating surface, and so forth.
Recording heads commercially produced are tested after fabrication for the purpose of confirmation of the printing quality they produce. In some cases, the rate of rejection is impractically large due to fluctuations in the printing quality according to the recording head products. Recording heads which showed inferior printing characteristics have been examined and it has been found that the unstable generation of the bubble was due to changes in the state of the bubble-generating surface or residue remaining on the bubble-generating surface. It has thus been confirmed that unstable bubble generation causes a fluctuation in the velocity or direction of the ink droplet discharged from the head, resulting in degradation of the printing quality.
A study has also been made to clarify the causes of the change in the surface state of the bubble-generating surface and the generation of residue on the bubble-generating surface, and it has been found that these are attributable to the following causes.
(1) The state of the bubble-generating surface tends to change during patterning due to a reaction between a photo-resist and the bubble-generating surface.
(2) Deposition of residue is caused by incomplete separation of the photo-resist after patterning.
(3) The state of the bubble-generating surface tends to change as a result of a reaction between the bubble-generating surface and a photosensitive resin which is used in a process for forming liquid channels leading to the discharge ports.
(4) The photosensitive resin mentioned above tends to remain as residue on the bubble-generating surface due to incomplete removal.
(5) The bubble-generating surface tends to be contaminated by various resins used in packaging or the mounting process such as a flux resin and sealing resin which remain as residue on the bubble-generating surface.
It might be possible to overcome the aforementioned problem by eliminating causes (1) to (5) mentioned above. Such a measure, however, is impractical and extremely difficult to conduct due to the necessity for changing the materials used for producing the head, as well as alteration of production processes. In addition, production cost is raised due to the use of special materials.